On the photoelectron spectrum of p-benzoquinone

A high-resolution photoelectron spectrum of p-benzoquinone in the low energy ~9.5–11.5 eV! region is reported and analyzed with the aid of simulations based on high-level ab initio calculations. The results generally support the notion that the two prominent spectral features in this region are each due to a pair of final ion states. The lower energy feature beginning near 10 eV is due to oxygen lone-pair ionizations, while that beginning near 11 eV comes from p electron removal. Contrary to previous interpretations of the spectrum, however, the results of this study indicate that the two p states are nearly degenerate, with the strongest peak in the photoelectron spectrum representing a convolution of the corresponding pair of 0–0 ionizations. © 2001 American Institute of Physics. @DOI: 10.1063/1.1381575#